jeremyb_nz

Hmmm, wondering why steel frames are generally brazed rather than tig welded? is it the setup cost thats the factor or am I missing something?

I'm keen to start building some frames and am looking at buying a TIG

andrewstcyr

Been welding for years man. Brazing is very quick and extremely easy to do where tig welding is a difficult process that takes lots of practice to become good at. TIG welding is by far stronger and it allows you to weld all kinds of different exotic metals with the correct setup where brazing is limited to a handful of applications. Fit-up of the joints with brazing will be a lot more critical to get maximum strength.

jeremyb_nz

Strength was definately a concern as I want to make MTB and BMX frames which will need to take a beating, I don't mind spending the time learning to TIG, I'm fascinated with the process and metalwork in general, but being a computer geek haven't had the practical experience... I've done a mig course in the past and the general thing seems to be spend time on welding and practice on lots of scrap until you're confident, the Covell video makes it look super easy but I realise the guys a pro!

Revtor

If im not mistaken, brazing with lugs (wide overlap) will be just as strong as a tig welded frame (thin bead on thin tubing)

~Steve

RedSerotta

Technically, welding is stronger than brazing. The chemical and physical processes that occur are fundamentally different. Ever try to "undo" a weld? Not going to happen. But if you put a torch on a braze, the material can just ooze right off. However, excellent brazes are more than enough for most bike frames. I love to mig and tig (mostly art and cars, not bikes) so why not?

Scooper

I think you're forgetting the strength added to a brazed lugged joint by the lug itself. There is objective evidence that brazed lug construction is stronger than TIG welded construction. While the testing at U.C. Davis was done before air hardening steel tubing like Reynolds 853 was available, the argument regarding stress risers in TIG welded joints making them more prone to failure is still valid.

seeker333

You are misinformed.

Probably 99% of all steel frames made since ~1992 are tigged. Nowadays only high end steel frames are brazed - most of these are lugged, far fewer are fillet brazed.

Brazing can be done at relatively low cost. You can buy a propane torch and brazing rod at most hardware stores for as little $20US and repair a joint, attach a boss, etc. However, good builders have much fancier tube milling and brazing equipment and use more expensive, harder-to-find materials.

Nessism

That blurb from Spectrum is full of inconsistencies. For example regarding the UCD study, first they say "They concluded that all three joining techniques (TIG, Lug, Fillet Brazed), done properly, are clearly of sufficient strength for the purpose of bicycle frame construction." Next they go to say, "Frames built with silver soldered lugs will last longer than those that are fillet brazed and considerably longer than those that are welded."

Honestly, the joining technique does not matter as long as the joining is done properly. TIG is very popular since it's cheapest. It's also slightly lighter which is important to many people. Frame will ride the same either way - it's mostly about looks and cost.

Scooper

Nessism, I agree with everything you say; my post was primarily to object to the characterization of TIG welding as inherently "far stronger" than brazing.

I'd like to find a copy of the Bicycle Guide article Tom Kellogg refers to on the Spectrum website.

NoReg

One thing I am suspicious of in that test is how they tested the joints. Bikes operate as a system, and tube deflection is kept to a minimum because the parts are often triangulated. It's tempting when testing joints to test them unsupported, as t-junctions, different failure rates in that format are certainly noteworthy for certain applications, but not necessarily all that meaningful for frames themselves. Without he original article, hard to say what any of it means. Does make one wonder why nothing more quoteworthy has emerged on the subject in 25 years. We have new welding machines, tubes, fillers, etc...

The major flaw in the test is that there is no attempt to deal with the weight issue, at least not in what is reproduced in the link. Sure they accept that lugs are heavier by a few ounces on a bicycle basis, on a joint basis that is massive. The joint in tig is a little strip a few 1/16ths wide that runs around the tube junction. The lug (or brazed joint) isn't a few ounces more on maybe a 6 pound frame, it's a few ounces more vs. something that ways not an ounce at all. If we used as much structure in our welds as is used in lugs the whole scenario would change. Sure gussets are not appreciated in the bike world, or roadie world, but that is one option that is being ignored here. Another option might be much more enhanced butting in TIG tubes, though that does not seem necessary, it would probably win a few tests, though.

jeremyb_nz

I guess I should have said frames made by home builders or low volume shops

Revtor

its simpler to braze, less catastrophic if you mess up a joint, more ability to personalize, adds areas for custom paint, looks classic.

~Stv

RedSerotta

Scoop,

My mistake. Being more of a metalworker and less of a framebuilder, I had neglected to remember that brazed frames are lugged, adding even more strength. I was speaking on more of a metal-metal level, so I stand corrected. Thanks.

Hocam

That's not an inconsistency.

Sufficient strength is different from longevity.

In what I've been reading and from what I can add from the mechanics of materials engineering classes I've taken, fillet brazed joints do not create stress risers, unlike the highly heterogeneous surface and interface of TIGed joints. Also, the transition from lug to tube will create a stress riser but seems far away enough from the joint to be less of a problem. However, I've seen several older racing frames broken at the edge of the lug on the chainstay, seat tube and downtubes all at the bottom bracket.
I don't think TIGed frames have been around long enough for failures to really start occuring yet and there just weren't nearly as many racing frames with thin tubes and fillet brazed joints for a good comparison to lugs.

NoReg

"I don't think TIGed frames have been around long enough for failures to really start occuring yet and there just weren't nearly as many racing frames with thin tubes and fillet brazed joints for a good comparison to lugs."

That of course, is one advantage of TIG, nothing is really around or kept long enough to be worth putting together with lugs. People ride completely new bikes every season or race. Longevity really isn't important any more. At some point though, when the aircraft factories were forced to give up gas welding in favor of TIG, for OSHA concerns, I'm guessing someone looked into the fatigue issues.

I spend probably more time in the Walmart bike area while the kids are buying Barbies, than I do in the LBS. I see all these dual suspension bikes for a hundred or so dollars, and look at the welding, which often looks pretty neat. I don't care if they are using slave labour, the consumable costs alone, make it improbable these bikes are being TIG welded. Some of them have several feet of aluminum welding on them. I suspect many of the "TIG" welded bikes we see are migged or robot welded, which doesn't mean they are badly welded. TIG is dependant on operator skill and there is a wide varience in the skill of various people who do it. Most consumers don't know this, don't know good welding from bad. Aren't aware there are master welders out there who produce a product that is many rungs on the ladder above the average "name" maker. To say that a TIG weld broke really doesn't tell us anything.

Bike building is a business with some full time makers, and a lot of skilled dabblers. Welding is a whole separate art. Unless a builder wants to also learn welding, the cost and skill curves are really too steep for welding. It does depend whether the builder is a welder first or a bike maker. I know some welders who can make a bike with cheaper welding technologies, but most people aren't in their class, and almost all bike builders are a little unimaginative about that kind of inovation, they just want to know what everyone else is doing.

Probably almost anyone could learn to weld a bike frame, there is a big difference between that and being good enough to teach yourself, explore until you find your own machine settings, and take the art to the point where you would put your house behind it. And in any case there are many place where you need a gas torch anyway in bike building so most people sign up for that alone since it saves them a few grand in tools. My welding hood cost more than my OA gas rig.

"I had neglected to remember that brazed frames are lugged, adding even more strength"

There is also the fascinating art of fillet brazing which uses braze as the joining material, no lugs. We have three comon methods: Welding, Lug, and Fillet braze. None is stronger than any other, since any one can be designed to be strong enough. There are great bikes being made in all three. Fillet and TIG have the advantage of unlimited geometry in the joints. But lugs are available for a lot of classic designs. Arguing about which is better seems to be dropping off in the frame comunity where some builder do both like Gordon, or some bikes end up using all three methods. Like for instance the Henry James MTB lug that uses a fillet for the chain stays. Or the lug guy who assembles custom lugs with tig. Custom makers are more banding together than fighting over this stuff any more.

NoReg

"the Covell video makes it look super easy but I realise the guys a pro!"

It is sorta easy. It probably won't take you too long to turn out a good weld in something, but move over to the next coupon and it may be crap again. I have tought myself, and one gets the hang of it reasonably quickly, but it still will stiff me when I move to a different situation, and I have to redial. There is an old idea in science about only changing one variable at a time when doing experiments so one can tell what changes are leading to what results. If you move from 1/8" cold rolled, to .049 4130, you have changed, your base metal, your filler rod size, filler material, possibly your tungsten, you amperage, pulse, your gap, your flow rate, possibly your cup. Maybe you nail it right out of the blocks, and it's cool or maybe you just keep trying stuff for months and you never get it. Then it turns out the problem was the gas, or the way one metal reacted to background heat. Or maybe one needed a purge to keep the temp from fluctuating, or the sugaring under control, even though it worked in the thicker material without.

Now if you answer telephones at Bike Friday and they say you need to build a frame to keep your job. You will (I assume) walk into a shop where all that stuff has been worked out and they maybe watch you and give you a few tips, and if you slow down travelling on the tighter tubes, maybe someone reaches over and cools the amps. "Hey this is easy !"

I'm still hacking it up welding. I have made a few nice things, but I am still on the steep part of the learning curve. Welding is great though. Even a bad welder can get some payback. Just a few weeks back we really needed to mow the lawn before a storm, the mower wasn't working, and I pinned it down to a pipe brace that was held in place with one tack, and it had broken. I had to do the repair out of doors, so I used stick which is an alternative my TIG power source supports. I got it back together in a few minutes, and saved a 200 dollar reel mower.

cujet

I do aircraft component welding. I also do certified brazing on structural components. Gas welding, Tig, stick and brazing along with many other forms of welding can be strong enough when the joint is engineered properly. Your car is likely spot welded!

On vintage Brittish race cars brazing was used to attach the suspension to the tubes. It was done in a unique way that still has merrit today. The tubes were tacked with braze in a "T" coming off the frame. Then brass was used to make the entire assy large enough to become a solid post rather than a "T".

The reason was that the low heat used while brazing did not affect the temper of the frame. When those cars crashed, they bent up like a pretzel, but never ever cracked or broke. Quite unlike American race cars of the time. The advantage was significant and allowed cars like the Lotus to weigh much less and outperform the competition.

Personally, I like tig the best.

Chris